Direct conversion of sulphide and sulphate minerals to SO₂ for isotope analyses

Sulphide and sulphate minerals mixed with V₂0₅ and SiO₂, were heated in a vacuum at 950°C for 15 minutes, The evolved SO₃was converted to SO₂by reaction with metallic Cu for sulphur isotope determinations. This technique yields SO₂of consistent oxygen isotope composition regardless of whether sulphide or sulphate is converted. The reproducibilities of sulphur conversion and S₃₄S values were 98 ±5% and ±0,2%, respectively. The technique is particularly suitable for small samples. Successful isotope determinations have been obtained with natural samples containing less than I mg S. In some cases, variations in 5₃₄S of 2% have been found for single grains analysed from a small specimen.